Hi
----- Original Message -----
> On 07/06/17 12:16, Marc-André Lureau wrote:
> > Add vmcoreinfo ELF note if vmcoreinfo device is ready.
> >
> > To help the python script, add a little global vmcoreinfo_gdb
> > structure, that is populated with vmcoreinfo_gdb_update().
> >
> > Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> > ---
> > scripts/dump-guest-memory.py | 40 ++++++++++++++++++++++++++++++++++++++++
> > hw/acpi/vmcoreinfo.c | 3 +++
> > 2 files changed, 43 insertions(+)
> >
> > diff --git a/scripts/dump-guest-memory.py b/scripts/dump-guest-memory.py
> > index f7c6635f15..2dd2ed6983 100644
> > --- a/scripts/dump-guest-memory.py
> > +++ b/scripts/dump-guest-memory.py
> > @@ -14,6 +14,7 @@ the COPYING file in the top-level directory.
> > """
> >
> > import ctypes
> > +import struct
> >
> > UINTPTR_T = gdb.lookup_type("uintptr_t")
> >
> > @@ -120,6 +121,20 @@ class ELF(object):
> > self.segments[0].p_filesz += ctypes.sizeof(note)
> > self.segments[0].p_memsz += ctypes.sizeof(note)
> >
> > +
> > + def add_vmcoreinfo_note(self, vmcoreinfo):
> > + """Adds a vmcoreinfo note to the ELF dump."""
> > + chead = type(get_arch_note(self.endianness, 0, 0))
> > + header =
> > chead.from_buffer_copy(vmcoreinfo[0:ctypes.sizeof(chead)])
>
> Maybe it's obvious to others, but I would have been helped a lot if a
> comment had explained that you are creating a fake note (with 0 desc
> size and 0 name size) to figure out the size of the note header. And
> then you copy that many bytes out of the vmcoreinfo ELF note.
>
ok
> > + note = get_arch_note(self.endianness,
> > + header.n_namesz - 1, header.n_descsz)
>
> Why the -1?
because get_arch_note() adds + 1 (supposedly for the ending \0, see also
add_note())
>
> ... I think I'm giving up here for this method. My python is weak and I
> can't follow this too well. Please add some comments.
I simplified a bit the code now, I was also discovering some ctype usage.
> More comments below:
>
> > + ctypes.memmove(ctypes.pointer(note), vmcoreinfo,
> > ctypes.sizeof(note))
> > + header_size = ctypes.sizeof(note) - header.n_descsz
> > +
> > + self.notes.append(note)
> > + self.segments[0].p_filesz += ctypes.sizeof(note)
> > + self.segments[0].p_memsz += ctypes.sizeof(note)
> > +
> > def add_segment(self, p_type, p_paddr, p_size):
> > """Adds a segment to the elf."""
> >
> > @@ -505,6 +520,30 @@ shape and this command should mostly work."""
> > cur += chunk_size
> > left -= chunk_size
> >
> > + def phys_memory_read(self, addr, size):
> > + qemu_core = gdb.inferiors()[0]
> > + for block in self.guest_phys_blocks:
> > + if block["target_start"] <= addr < block["target_end"]:
>
> Although I don't expect a single read to straddle phys-blocks, I would
> prefer if you checked (addr + size) -- and not just addr -- against
> block["target_end"].
done
>
> > + haddr = block["host_addr"] + (addr -
> > block["target_start"])
> > + return qemu_core.read_memory(haddr, size)
> > +
> > + def add_vmcoreinfo(self):
> > + if not gdb.parse_and_eval("vmcoreinfo_gdb_helper"):
> > + return
> > +
> > + addr =
> > gdb.parse_and_eval("vmcoreinfo_gdb_helper.vmcoreinfo_addr_le")
> > + addr = bytes([addr[i] for i in range(4)])
> > + addr = struct.unpack("<I", addr)[0]
> > +
> > + mem = self.phys_memory_read(addr, 16)
> > + (version, addr, size) = struct.unpack("<IQI", mem)
> > + if version != 0:
> > + return
> > +
> > + vmcoreinfo = self.phys_memory_read(addr, size)
> > + if vmcoreinfo:
> > + self.elf.add_vmcoreinfo_note(vmcoreinfo.tobytes())
> > +
> > def invoke(self, args, from_tty):
> > """Handles command invocation from gdb."""
> >
> > @@ -518,6 +557,7 @@ shape and this command should mostly work."""
> >
> > self.elf = ELF(argv[1])
> > self.guest_phys_blocks = get_guest_phys_blocks()
> > + self.add_vmcoreinfo()
> >
> > with open(argv[0], "wb") as vmcore:
> > self.dump_init(vmcore)
> > diff --git a/hw/acpi/vmcoreinfo.c b/hw/acpi/vmcoreinfo.c
> > index 0ea41de8d9..b6bcb47506 100644
> > --- a/hw/acpi/vmcoreinfo.c
> > +++ b/hw/acpi/vmcoreinfo.c
> > @@ -163,6 +163,8 @@ static void vmcoreinfo_handle_reset(void *opaque)
> > memset(vis->vmcoreinfo_addr_le, 0,
> > ARRAY_SIZE(vis->vmcoreinfo_addr_le));
> > }
> >
> > +static VMCoreInfoState *vmcoreinfo_gdb_helper;
> > +
> > static void vmcoreinfo_realize(DeviceState *dev, Error **errp)
> > {
> > if (!bios_linker_loader_can_write_pointer()) {
> > @@ -181,6 +183,7 @@ static void vmcoreinfo_realize(DeviceState *dev, Error
> > **errp)
> > return;
> > }
> >
> > + vmcoreinfo_gdb_helper = VMCOREINFO(dev);
> > qemu_register_reset(vmcoreinfo_handle_reset, dev);
> > }
> >
> >
>
> I guess we don't build QEMU with link-time optimization at the moment.
>
> With link-time optimization, I think gcc might reasonably optimize away
> the assignment to "vmcoreinfo_gdb_helper", and "vmcoreinfo_gdb_helper"
> itself. This is why I suggested "volatile":
>
> static VMCoreInfoState * volatile vmcoreinfo_gdb_helper;
>
> Do you think volatile is only superfluous, or do you actively dislike it
> for some reason?
Yeah, I am not convinced volatile is the best way, but nor is static.
Let's export it?
